This application claims a priority from German application 101 19 219.3, filed Apr. 20, 2001, and the contents of that German application are incorporated by reference herein.
The present invention relates to an electronic device with a housing for attachment to a pane of a motor vehicle, wherein the coupling of the housing to the vehicle pane is effected through a coupling medium of a flexible rubber- or gel-like material.
When adapting electronic devices to panes of vehicles, for functional and/or design-related reasons it is necessary to directly couple the electronic devices to the vehicle panes through a coupling medium typically of a flexible rubber- or gel-like material, like Silgel, for example, or a molded silicone part.
The coupling medium may serve the purposes of optical as well as mechanical coupling of the electronic device (such as, for example, rain sensor, light sensor, pre-crash sensor, camera systems, compass sensor, toll sensor, parking sensor circuits, sensor circuits for adaptive velocity control etc.). These devices are either directly agglutinated (adhered) on the pane surface by the coupling medium, or they are pressed against the pane by a continuously-acting spring element, with the coupling medium to be utilized not applying any holding force.
In this context, the adaptation of a particular device to a surface of a vehicle pane is important. Panes of vehicles generally have deviations (tolerances) with regard to their curvature geometry. In consequence, the coupling medium has to compensate for these tolerances in the panes in order to ensure the function and/or the desired outer appearance (design) of the device to be coupled. This compensation for tolerances by the coupling medium is subject to limitations.
For functional and/or process-related reasons during manufacturing, the structure of the coupling medium is restricted. Thus, the shape of the coupling medium can in general be realized only for a limited range of pane curvatures. This has the consequence that a clean and, above all, bubble-free coupling is highly problematic for panes having greatly differing curvatures.
Especially when the pane surfaces are greatly curved, there is the risk of enclosing air bubbles during the mounting of the device. Coupling media, like for example Silgels, can eliminate smaller air bubbles to a certain extent, depending on time and contact pressure. Larger air bubbles, however, will remain within the region of the coupling medium. Through contact pressure of the spring element, a balanced pressure ratio between coupling medium and enclosed air bubble is reached. Due to a viscosity typical for such coupling media, an interior pressure inside the coupling medium can be distinctly higher in an edge region of an area to be coupled than in a region of the enclosed air bubble.
This effect directly depends on the shape of the surface of the device to be coupled and the pane curvature within the mounting area. In consequence, the enclosed air bubble, due to its tendency to expand, will typically migrate to the region between the coupling medium and the pane having the lowest internal pressure in the coupling medium. If the device contour is round, for example, this causes the enclosed air bubble to migrate to the middle of the coupling area during adaptation to a curved pane. Thus, the air bubble is uniformly surrounded by coupling material at a higher internal pressure and hence cannot escape in order to expand outside the region of the coupling medium to atmospheric pressure.
The tendency to enclose air bubbles as well as the location of their occurrence depends directly on the pane curvature and the structure of the device surface, including the coupling medium.
It is an object of this invention to provide an electronic device structured such that it can be coupled to a vehicle pane without air bubbles.
According to principles of the invention, an exhaust duct connected to the ambient air is located in a region of potential bubble formation between the vehicle pane and a coupling medium.
The surface of the device and/or the coupling medium is therefore advantageously shaped in such a way that bubbles that might be formed during mounting always have a chance to escape (exhaust).